1. Field of the Invention
This invention relates generally to vehicle air conditioning systems, and more particularly to a vehicle air conditioning system dehumidifier for dehumidifying ventilation air via a drying agent.
2. Description of the Related Art
In automotive vehicle air-conditioning systems, a passenger compartment is typically heated by utilizing warm water from an engine as a heat source. However, in recent years, as vehicle engines have become more efficient, the resulting temperature of the engine water has decreased, causing the heating capacity of the systems to often become insufficient.
To eliminate the above heating capacity deficiency, many conventional systems increase the percentage of inside air taken in to reduce the heating load. Specifically, an auxiliary door for mixing inside air with outside air has been added to a system inside/outside air switching box, or an inside/outside air 2-layer mode wherein only outside air is delivered to a defroster outlet side, and only inside air is delivered to a foot outlet side.
However, even in this inside/outside air 2-layer mode, when the percentage of inside air exceeds 50%, window fogging caused by increased humidity inside the passenger compartment occurs. Therefore, to reduce the heat load by increasing the percentage of re-circulated inside air and to simultaneously prevent window fogging, the atmosphere inside the passenger compartment must be dehumidified.
In Japanese Patent Application Laid-open No. H.9-156349, the present inventors have proposed dehumidifying the interior of the passenger compartment by means of a dehumidifier which utilizes a drying agent. However, because the amount of water adsorbed per unit of drying agent is small, a large overall amount of drying agent is necessary to obtain a required dehumidifying capacity. As a result, various problems arise, such as increased installation space required by the system as a whole due to the volume of the drying agent, increased airflow resistance presented by the drying agent, and increased energy required to regenerate the drying agent.
Also, a granular drying agent such as silica gel or zeolite is generally used as the drying agent. Thus, as water from passenger compartment air is adsorbed onto the drying agent, condensation of water vapor occurs and heat of condensation is produced. As a result, the temperature of the drying agent is raised by this heat of condensation, and the dehumidifying capacity of the drying agent consequently decreases.